3 ms·

I doubt it. Raptor isn't a great deep space engine. It's ISP is a good bit lower than hyrdalox engines.

bryanlarsen 4y ago
Hydralox is worst of both worlds. To get out of gravity well thrust/weight is key, and Raptor is king at that. In deep space ISP is key, and ion thrusters are way more efficient than hydrolox at that. People don't realize that SpaceX is perhaps the world's largest manufacturer of ion thrusters since they use them on Starlink.
- avmich 4y ago
  Storage time is also important, and it's likely easier to store long term (Earth-Mars flight time is months) mid-cryogenic LOX and liquid methane rather than deep-cryogenic LH2.
- adgjlsfhk1 4y ago
  "To get out of gravity well thrust/weight is key" this isn't really true. TWR matters a lot for the first stage, but by the seccond stage, higher ISP and lower TWR is worth it as long as thrust is reasonable. ion thrusters are great for light unmanned probes but anything heavy needs higher thrust and hydralox is key for that. Ion propulsion is also pretty much worthless past jupiter since you can't get enough electricity.
  - bryanlarsen 4y ago
    Past Jupiter hydrolox is unusable because of boil-off issues. The best option past Jupiter is nuclear electric, aka ion propulsion. If you need both thrust & efficiency, a large number of ion thrusters is often a good option.
Me1000 4y ago
ISP is like fuel milage, and the economics change drastically when there's infrastructure in place. Having an abundant source of propellant near a celestial body with a much smaller gravity well (Mars) could easily change the economics and practicality of which fuels make sense for different missions. Put another way, we might one day look at Starship as a big rig semi truck (though the ISP of Raptor is actually really good while a big rig's is very much not). The fuel efficiency isn't really that important. I think (or hope at least) we're far away from being able to really see how much space access is going to change if Starship actually pulls off what they're trying.
- adgjlsfhk1 4y ago
  The big difference between ISP and millage is that ISP has exponential effects.
jvanderbot 4y ago
Yes, but the economy of scale makes it much better than alternatives for now. (Cost wise).

Hydralox is worst of both worlds. To get out of gravity well thrust/weight is key, and Raptor is king at that. In deep space ISP is key, and ion thrusters are way more efficient than hydrolox at that. People don't realize that SpaceX is perhaps the world's largest manufacturer of ion thrusters since they use them on Starlink.

avmich 4y ago
Storage time is also important, and it's likely easier to store long term (Earth-Mars flight time is months) mid-cryogenic LOX and liquid methane rather than deep-cryogenic LH2.
adgjlsfhk1 4y ago
"To get out of gravity well thrust/weight is key" this isn't really true. TWR matters a lot for the first stage, but by the seccond stage, higher ISP and lower TWR is worth it as long as thrust is reasonable. ion thrusters are great for light unmanned probes but anything heavy needs higher thrust and hydralox is key for that. Ion propulsion is also pretty much worthless past jupiter since you can't get enough electricity.
- bryanlarsen 4y ago
  Past Jupiter hydrolox is unusable because of boil-off issues. The best option past Jupiter is nuclear electric, aka ion propulsion. If you need both thrust & efficiency, a large number of ion thrusters is often a good option.

Me1000 4y ago

ISP is like fuel milage, and the economics change drastically when there's infrastructure in place. Having an abundant source of propellant near a celestial body with a much smaller gravity well (Mars) could easily change the economics and practicality of which fuels make sense for different missions. Put another way, we might one day look at Starship as a big rig semi truck (though the ISP of Raptor is actually really good while a big rig's is very much not). The fuel efficiency isn't really that important. I think (or hope at least) we're far away from being able to really see how much space access is going to change if Starship actually pulls off what they're trying.

adgjlsfhk1 4y ago
The big difference between ISP and millage is that ISP has exponential effects.

jvanderbot 4y ago

Yes, but the economy of scale makes it much better than alternatives for now. (Cost wise).